In lithography, the progressive downsizing of device dimensions, the apertures used in the systems, reach a situation where there are precise, area and location energy passing openings, in a member, that is relatively opaque to the energy and that member is so thin that avoiding damage to the member in fabrication, while providing support both in fabrication and in use, becomes difficult to achieve. The difficulty becomes increasingly acute where the aperture becomes a component in a simulation tool used in selecting the equipment that makes up the lithography system.
Lithography tools involving such systems have come to be known in the art as Aerial Image Measurement Systems (AIMS). Such tools allow the user to simulate a wide variety of processes by providing the ability to vary such unique parameters as wavelength and system optical properties such as numerical aperture. A critical component of any lithography system is in aperture which emulates the optical components in the system. Such an aperture would be ideally infinitely thin, perfectly smooth, exactly normal to the optical path, perfectly flat, and exactly shaped (a perfect circle for instance). A variety of aperture image shape openings such as the circle, and such patterns as double adjacent “D” openings, dual positioned circle openings and quad positioned opening patterns, are currently receiving attention in the art. Of the techniques for making the apertures at the present state of the art not all the patterns can be fabricated equally well.
At the present state of the art the apertures for these tools have traditionally been made by forming openings through metal foil that is typically 10 to 50 micrometers thick by such fabrication operations as mechanically punching and drilling. In general mechanical techniques involving punching, drilling and milling involve deformation and smearing of the thin member material resulting in image fidelity deterioration or damaging flatness so that use is mostly at dimensions of 100 micrometers or more. There are also wet etch techniques being investigated in the art but these techniques encounter difficulty resulting from the need for thinness so that minimum feature size and image resolution becomes approximately the thickness at the aperture. Investigations are taking place using photomasking technology for images in chromium on quartz. Such a technique introduces quartz as an additional optical component and would be expected to introduce an uncontrollable variable in short wavelength applications.